A transfer apparatus of the general type with which the present invention is concerned is disclosed in the U.S. Pat. No. 4,553,444. The apparatus disclosed in that patent includes a pair of fixed parallel tracks upon which a shuttle carriage is mounted for power driven movement longitudinally of the tracks from one end of the tracks to the other. Although not disclosed in detail in that patent, which is primarily directed to the mechanism employed to drive the shuttle carriage, a work piece holder is mounted upon the shuttle carriage. In a typical application, the transfer apparatus is positioned to extend between two machines which perform successive operations upon a work piece. The shuttle carriage is positioned at the end of its track adjacent the first machine and an automatic or robotic device is employed to extract a work piece from the first machine and load the work piece onto the work holder of the transfer apparatus, which then drives the shuttle carriage with the work piece to the opposite end of the transfer unit. A second automatic device then removes the work piece from the shuttle carriage and loads it into the second machine.
Because the loading and unloading of the transfer apparatus is performed by automatic devices, it is essential that the work holder of the transfer unit be precisely positioned at each end of its stroke to be in a proper orientation and alignment with the loading or unloading device. Where the production line in which the transfer apparatus is employed handles only work pieces of single configuration, problems of establishing the desired alignment between the transfer unit and the loading and unloading devices are simply solved by the initial set up of the unit. However, particularly in automotive related industries, present day practice requires that many production lines, particularly those employ machines involving a large capital investment, be capable of rapid conversion from production of one part to the production of a different part. Such a change over, in addition to the required modification of the tooling, can, and usually does, require modifications to the loading and unloading apparatus and changes to the work holder structure and its orientation upon the transfer unit, and possible a relocation of the end positions of the shuttle carriage.
One example of such a production line is one which is employed to stamp inner door panels for automotive vehicle doors. These inner door panels are employed to mount the door latching and window operating mechanisms and are of a complex shape such that the work piece blank passes through several successive stamping operations before it is finished. Transfer units of the general type referred to above are employed to transfer the work piece blank from one press to the next. Typically, two or more different inner door panel configurations are required for each different model of automobile- right and left handed configurations for two door automobiles, and right and left front and rear door configurations for four door automobiles.
Press lines for stamping parts of such complex shape include a series of relatively large presses fixedly mounted on the shop floor in spaced relationship to each other along a straight line. The transfer units extending between adjacent presses will have their longitudinal centerlines aligned with the straight line path through the presses. Where it is intended that the line will be shifted at fairly frequent intervals from production of one part to production of a different part, to accomplish a quick change is set up, the loading and unloading devices are provided with quick change modular work piece gripping heads, and a matched set of work piece holders are provided for the transfer unit, again with quick change couplings accommodating rapid removal and replacement upon the shuttle carriage of the transfer unit. By appropriate design, these matched pairs of work piece grippers and work piece holders will minimize or eliminate the necessity of reorientation or realignment of the transfer unit with its associated loading and unloading devices upon conversion from the handling of one part to the handling of another.
However, where the line must be capable of handling several different parts of differing sizes, shapes and configurations, it is frequently necessary to shift the orientation of the part between successive presses. Loading of the part upon the work holder on the shuttle carriage may, for example, be most conveniently accomplished if the work holder is inclined toward the adjacent side of the press from which it receives the part and is reversely inclined for the unloading operation at the opposite end of its stroke. Also, the geometry of the part may be such that shifting the part transversely of its path of travel between the two presses may be desirable.
Shifting of the position of the part relative to the fixed frame of the transfer apparatus during transit from one end of the apparatus to the other will normally require some powered device mounted upon the shuttle carriage, and the supply of power to these actuating devices will require the coupling of an electrical cable or pneumatic hose to some point on the carriage. In that the path of travel of a typical shuttle carriage may be ten feet or more, the handling of these power cables or supply lines, which must be connected at one end to a stationary power outlet presents a problems. Guidance and handling of a single line extending from a fixed supply location to the moving carriage can easily be handled with an articulated cable guide of well known construction. However, when two or more power supply lines or cables must be attached at one end to a movable shuttle carriage at locations on the carriage which are in turn moveable relative to one another, a single cable guide is not sufficient and two or more cable guides leading to relatively moveable points on the shuttle present an exceedingly complex design problem.
The present invention is directed to a transfer unit which includes a work holder mounted upon a shuttle carriage for independent adjustable movement in two types of movement relative to the shuttle carriage while requiring but a single supply cable connection to the carriage.